iphone se and itunes

You need to be running Windows 7 on a PC or OS X 10.9.5 on a Mac, plus iTunes 12.6 (the latest version) in order to sync a device that is running iOS 10.

If you meet those requirements, look here for help.

If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support

Did you go through all of the steps in the support article yet? There are quite a few things that you can check first before you need to contact Apple. However, if you feel more comfortable going to an Apple Store for help, make an appointment and take the phone to them.

If you are a Windows user, you might find this to be helpful,

Troubleshooting issues with iTunes for Windows updates